Imprint lithography

ABSTRACT

A method of determining a position of an imprint template in an imprint lithography apparatus. In an embodiment, the method includes illuminating an area of the imprint template in which an alignment mark is expected to be found by scanning an alignment radiation beam over that area, detecting an intensity of radiation reflected or transmitted from the area, and identifying the alignment mark via analysis of the detected intensity.

This application is the United States national phase entry of PCT patentapplication no. PCT/EP2011/050246, filed Jan. 11, 2011 (published as PCTpatent application publication no. WO 2011/107302), which claims thebenefit under 35 USC §119(e) of U.S. provisional patent application no.61/310,077, filed on Mar. 3, 2010, the contents of each of the foregoingdocuments incorporated herein in its entirety by reference.

FIELD

The present invention relates to imprint lithography.

BACKGROUND

In lithography, there is an ongoing desire to reduce the size offeatures in a lithographic pattern in order to increase the density offeatures on a given substrate area. In photolithography, the push forsmaller features has resulted in the development of technologies such asimmersion lithography and extreme ultraviolet (EUV) lithography, whichare however rather costly.

A potentially less costly road to smaller features (e.g. micron size ornanometer sized features, e.g., less than or equal to 10 microns, lessthan or equal to 1 micron, less than or equal to 50 nm, less than orequal 25 nm or less than or equal to 10 nm sized features) that hasgained increasing interest is so-called imprint lithography, whichgenerally involves the use of a “stamp” (often referred to as an imprintlithography template) to transfer a pattern onto a substrate. Anadvantage of imprint lithography is that the resolution of the featuresis not limited by, for example, the emission wavelength of a radiationsource or the numerical aperture of a projection system. Instead, theresolution is mainly limited to the pattern density on the imprintlithography template.

Imprint lithography involves the patterning of an imprintable medium ona surface of a substrate to be patterned. The patterning may involvebringing together a patterned surface of an imprint lithography templateand a layer of imprintable medium (e.g., moving the imprint lithographytemplate toward the imprintable medium, or moving the imprintable mediumtoward the imprint lithography template, or both) such that theimprintable medium flows into recesses in the patterned surface and ispushed aside by protrusions on the patterned surface, to adopt thetopography of that patterned surface. The recesses define patternfeatures of the patterned surface of the imprint template. Typically,the imprintable medium is flowable when the patterned surface and theimprintable medium are brought together. Following patterning of theimprintable medium, the imprintable medium is suitably brought into anon-flowable or frozen state (i.e. a fixed state), for example byilluminating the imprintable medium with actinic radiation. Thepatterned surface of the imprint lithography template and the patternedimprintable medium are then separated. The substrate and patternedimprintable medium are then typically processed further in order topattern or further pattern the substrate. The imprintable medium may beprovided in the form of droplets on the surface of a substrate to bepatterned, but may alternatively be provided using spin coating or thelike.

Lithography typically involves applying several patterns onto asubstrate, the patterns being stacked on top of one another such thattogether they form a device such as an integrated circuit. Alignment ofeach pattern with a previously provided pattern is a significantconsideration. If patterns are not aligned with each other sufficientlyaccurately, then this may result in, for example, electrical connectionsbetween layers not being made. This, in turn, may cause the device to benon-functional. A lithographic apparatus therefore usually includes analignment apparatus which is intended to align each pattern with apreviously provided pattern.

SUMMARY

It is desirable to provide an imprint lithography alignment apparatusand method which is novel and inventive over the prior art.

According to an aspect, there is provided a method of determining aposition of an imprint template in an imprint lithography apparatus, themethod comprising illuminating an area of the imprint template in whichan alignment mark is expected to be found by scanning an alignmentradiation beam over that area, detecting an intensity of radiationreflected or transmitted from the area, and identifying the alignmentmark via analysis of the detected intensity.

According to an aspect, there is provided an imprint lithographyapparatus comprising an imprint template holder configured to hold animprint template, an alignment radiation beam outlet, a detector, and aprocessor, wherein the apparatus is configured to provide scanningmovement between the imprint template and an alignment radiation beamprovided by the alignment radiation beam outlet, such that the alignmentradiation beam illuminates an area of the imprint template in which analignment mark is expected to be found, the detector is configured todetect an intensity of radiation reflected or transmitted from the area,and the processor is configured to identify the alignment mark viaanalysis of the detected intensity.

According to an aspect, there is provided a method of obtaining coarsealignment of a substrate and an imprint template, the method comprisingilluminating an imprint template alignment grating using an alignmentradiation beam, providing relative movement between the substrate andthe imprint template in a first lateral direction, providing amodulation between the substrate and the imprint template in a secondlateral direction which includes a component that is perpendicular tothe first lateral direction, detecting modulation of the alignmentradiation when the relative movement between the substrate and theimprint template in the first lateral direction causes a substratealignment grating to overlap with the imprint template alignmentgrating, and analysing the detected modulation to determine a maximumoverlap between the substrate alignment grating and the imprint templatealignment grating, and to determine the relative positions of thesubstrate and the imprint template when the maximum overlap occurred.

According to an aspect, there is provided An imprint lithographyapparatus comprising an imprint template holder configured to hold animprint template and a substrate holder configured to hold a substrate,the imprint template holder and/or the substrate holder configured toprovide relative movement between the substrate and the imprint templatein a first lateral direction, and configured to provide a modulationbetween the substrate and the imprint template in a second lateraldirection which includes a component that is perpendicular to the firstlateral direction, an alignment radiation beam outlet configured toilluminate an imprint template alignment grating, a detector configuredto detect radiation reflected from the imprint template alignmentgrating and an adjacent substrate alignment grating, and a processorconfigured to determine a maximum of a modulation of the detectedreflected alignment radiation, and to determine a maximum overlapbetween the substrate alignment grating and the imprint templatealignment grating based on the determined maximum of the modulation, themaximum overlap providing coarse alignment of the substrate and theimprint template.

According to an aspect, there is provided an imprint template alignmentgrating comprising a low resolution grating formed from sets of lineswhich comprise high resolution gratings.

According to an aspect, there is provided an imprint template and asubstrate, the imprint template having a first imprint templatealignment grating and a second imprint template alignment grating, andthe substrate having a first substrate alignment grating and a secondsubstrate alignment grating, wherein the pitch of the first imprinttemplate alignment grating is smaller than the pitch of the secondimprint template alignment grating, and the pitch of the first substratealignment grating is smaller than the pitch of the second substratealignment grating.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will be described with referenceto the accompanying Figures, in which:

FIGS. 1 and 2 schematically depict examples of, respectively, hotimprint, and UV imprint lithography;

FIGS. 2 to 5 schematically shows a lithographic apparatus according toan embodiment of the invention;

FIGS. 6 and 7 schematically shows part of an imprint template and anintensity image which may be used by an embodiment of the invention;

FIGS. 8 and 9 schematically show use of imprint template alignmentgratings and substrate template alignment gratings according to anembodiment of the invention; and

FIGS. 10 to 13 schematically show alignment gratings according to anembodiment of the invention.

DETAILED DESCRIPTION

Examples of approaches to imprint lithography are schematically depictedin FIGS. 1 and 2.

FIG. 1 shows an example of so-called hot imprint lithography (or hotembossing). In a typical hot imprint process, a template 2 is imprintedinto a thermosetting or a thermoplastic imprintable medium 4, which hasbeen cast on the surface of a substrate 6. The imprintable medium 4 maybe, for example, resin. The resin, for instance, may be spin coated andbaked onto the substrate surface or, as in the example illustrated, ontoa planarization and transfer layer 8 of the substrate 6. When athermosetting polymer resin is used, the resin is heated to atemperature such that, upon contact with the template, the resin issufficiently flowable to flow into the pattern features defined on thetemplate. The temperature of the resin is then increased to thermallycure (crosslink) the resin so that it solidifies and irreversibly adoptsthe desired pattern. The template 2 may then be removed and thepatterned resin cooled. In hot imprint lithography employing a layer ofthermoplastic polymer resin, the thermoplastic resin is heated so thatit is in a freely flowable state immediately prior to imprinting withthe template 2. It may be necessary to heat a thermoplastic resin to atemperature considerably above the glass transition temperature of theresin. The template is pressed into the flowable resin and then cooledto below its glass transition temperature with the template 2 in placeto harden the pattern. Thereafter, the template 2 is removed. Thepattern will consist of the features in relief from a residual layer ofthe resin which may then be removed by an appropriate etch process toleave only the pattern features. Examples of thermoplastic polymerresins used in hot imprint lithography processes are poly (methylmethacrylate), polystyrene, poly (benzyl methacrylate) or poly(cyclohexyl methacrylate). For more information on hot imprint, see e.g.U.S. Pat. Nos. 4,731,155 and 5,772,905.

FIG. 2 shows an example of UV imprint lithography, which involves theuse of a transparent or translucent template which is transmissive to UVand a UV-curable liquid as imprintable medium (the term “UV” is usedhere for convenience but should be interpreted as including any suitableactinic radiation for curing the imprintable medium). A UV curableliquid is often less viscous than a thermosetting or thermoplastic resinused in hot imprint lithography and consequently may move much faster tofill template pattern features. A quartz template 10 is applied to aUV-curable resin 12 in a similar manner to the process of FIG. 1a .However, instead of using heat or temperature cycling as in hot imprint,the pattern is frozen by curing the imprintable medium 12 with UVradiation 14 that is applied through the quartz template 10 onto theimprintable medium 12. After removal of the template 10, the imprintablemedium 12 is etched. A particular manner of patterning a substratethrough UV imprint lithography is so-called step and flash imprintlithography (SFIL), which may be used to pattern a substrate in smallsteps in a similar manner to optical steppers conventionally used in ICmanufacture. For more information on UV imprint, see e.g. U.S. PatentApplication Publication No. 2004-0124566, U.S. Pat. No. 6,334,960, PCTPatent Application Publication No. WO 02/067055, and the article by J.Haisma entitled “Mold-assisted nanolithography: A process for reliablepattern replication”, J. Vac. Sci. Technol. B14(6), November/December1996.

Combinations of the above imprint techniques are possible. See, e.g.,U.S. Patent Application Publication No. 2005-0274693, which mentions acombination of heating and UV curing an imprintable medium.

FIG. 3 shows schematically an imprint lithography apparatus according toan embodiment of the invention. Referring to FIG. 3, a substrate 20bearing a layer of imprintable medium (not shown) is provided on asubstrate table 22. An imprint template 24 is held by an imprinttemplate holder 26. A output of actinic radiation 28 (for example, a UVradiation source) is provided above the imprint template holder 26. Alens 32 is provided between the actinic radiation output 28 and theimprint template holder 26.

The lithographic apparatus further comprises an output 34 (e.g., asource) which emits radiation (e.g. non-actinic radiation). The output34 will hereafter be referred to as the alignment beam output 34. Thealignment beam output 34 generates a collimated beam of radiation whichwill hereafter be referred to as the alignment radiation beam 35. Theoutput 34 may be configured to emit radiation at multiple wavelengths,which may for example include visible radiation and infrared radiation.In an embodiment, the output 34 is a radiation beam source. In anembodiment, the alignment radiation beam output 34 receives alignmentradiation from a source located outside of the lithographic apparatusand outputs the alignment radiation beam inside the lithographicapparatus.

A tip-tilt mirror 36 is provided above the imprint template holder 26.The tip-tilt mirror 36 can be tilted around the y and z axes, and isarranged to be moved between a plurality of orientations. Differentorientations of the tip-tilt mirror 36 may direct the alignmentradiation beam towards different alignment gratings 42, 43 provided onthe imprint template 24. It is not essential that the tip-tilt mirror bearranged to tilt around the y and z axes; any suitable axes may be used.Any other suitable beam directing apparatus may be used instead of thetip-tilt mirror, such as a combination of moveable mirrors.

The lithographic apparatus further comprises a beam-splitter 38 anddetector 40. The beam-splitter 38 is arranged to direct towards thedetector 40 a portion of the alignment radiation beam 35 which has beendiffracted from the substrate 20 and/or from the imprint template 24, asis explained below. The alignment radiation which is detected by thedetector 40 may be used to align the substrate 20 and the imprinttemplate 24.

The detector 40 may be capable of distinguishing between differentwavelengths of the alignment radiation beam 35. Where this is the case,the detector 40 may be able to detect and provide output signals for aplurality of wavelengths. Similarly, the detector 40 may be capable ofdistinguishing between different polarizations of the alignmentradiation beam 35. Where this is the case, the detector 40 may be ableto detect and provide output signals for a plurality of polarizations.

Signals which are output from the detector 40 are passed to a processor46. The processor 46 uses the signals to direct align the substrate 20with respect to the imprint template 24 (and/or to align the imprinttemplate with respect to the substrate). A controller 48 is connected tothe processor. The controller 48 controls the position of the substratetable 22 (and/or the imprint template holder 26) in the x, y and zdirections. The substrate table 22 may be moved, for example, by one ormore motors (not shown) of a type known to those skilled in the art. Theposition of the substrate table 22 may be monitored, for example, by oneor more interferometers or encoders (not shown) of a type known to thoseskilled in the art.

During alignment, there is no actinic radiation supplied from output 28(e.g., the source connected to the output is switched off or the actinicradiation is blocked) such that actinic radiation is not directed ontothe imprint template 24. A substrate 20 which has been provided with alayer of imprintable medium (not shown) is then placed on the substratetable 22. Coarse alignment of the substrate 20 and the imprint template24 may then be performed (described further below). The substrate tableis then moved until a target portion (e.g. a die) of the substrate 20 ispositioned beneath the imprint template 24, and the imprint templatealignment marks 42, 43 are located over alignment gratings 44, 45provided on the substrate.

Alignment of the target portion of the substrate 20 with the imprinttemplate 24 is achieved in the following manner. The tip-tilt mirror 36is oriented such that it directs the alignment radiation beam 35 towardsa first imprint template alignment grating 42. A proportion of thealignment radiation beam 35 will be diffracted from the imprint templatealignment grating 42, and a proportion of the alignment radiation beamwill pass onto the substrate alignment grating 44. A proportion of thealignment radiation beam 35 will then be diffracted by the substratealignment grating 44. The diffracted alignment radiation (i.e. alignmentradiation which has been diffracted from the imprint template alignmentgrating 42 or the substrate alignment grating 44) passes back to thetip-tilt mirror 36. The tip-tilt mirror directs the diffracted alignmentradiation towards the beam-splitter 38, which in turn directs thediffracted alignment radiation towards the detector 40. The detectorprovides output signals which pass to the processor 46.

The substrate table 22 (and substrate 20) move in the x-direction whilethe alignment measurement is being made. This may be considered to be anexample of a lateral movement (lateral movement may be considered tomean movement in a plane which is parallel or substantially parallel tothe surface of the substrate). The movement may be a scanning motionover a length that is normally (but not necessarily) one or more periodsof the substrate alignment grating 44. Alternatively, the movement maybe a modulation over a length which is less than the pitch of thesubstrate grating. As a result of this movement, the substrate alignmentgrating 44 moves beneath the imprint template alignment grating 42,thereby giving rise to a modulation of the diffracted alignmentradiation. This modulation is measured by the detector 40 and is passedto the processor 46. Properties of the modulation are linked to therelative position of the substrate alignment grating 44 and the imprinttemplate alignment grating 42, and these properties may thus be used toalign the substrate 20 and the imprint template 24.

The detector may measure the modulation at a plurality of wavelengths,and provide a plurality of output signals accordingly. Where this is thecase, the output signals are passed to the processor 46, which uses theoutput signals to determine the position of the substrate alignmentgrating 44 relative to the imprint template alignment grating 42.

Referring to FIG. 4, the tip-tilt mirror 36 is then moved to a neworientation, such that the alignment radiation beam 35 is directedtowards a second imprint template alignment grating 43 and associatedsubstrate alignment grating 45. Again, a portion of the alignmentradiation beam 35 is diffracted, and passes via the tip-tilt mirror 36and beam-splitter 38 to the detector 40. The substrate table 22 (andsubstrate 20) move with a scanning motion or modulation in thex-direction, thereby giving rise to a modulation of the diffractedalignment radiation. The detector 40 provides output signals which passto the processor 46. The processor 46 uses the signals to determine therelative position of the substrate alignment grating 45 and the imprinttemplate alignment grating 43.

The tip-tilt mirror 36 may then be moved to other orientations in orderto direct the alignment radiation beam 35 towards other alignmentgratings (not shown).

The processor 46 uses the signals output from the detector 40 todetermine the aligned position of the substrate 20 relative to theimprint template 24 (or of the imprint template 24 relative to thesubstrate 20). The aligned position may, for example, be the position inwhich a pattern provided on the imprint template 24 is aligned with apattern provided on the substrate 20 (e.g. a previously formed layer ofa die). Once the aligned position has been determined, the substrate 20and/or imprint template 24 is moved to the aligned position. This is maybe achieved, for example, by moving the substrate table 22 using amotor, while monitoring the position of the substrate table using aninterferometer. In addition to moving the substrate 20, the size of theimprint template 24 may be adjusted using one or more actuators (notshown).

Once the substrate and the imprint template have been aligned, theimprint template holder 26 is lowered (and/or the substrate table israised) so that the imprintable medium flows into pattern recesses ofthe imprint template 24. As shown in FIG. 5, the radiation output 28provides a beam of actinic radiation 29 which is directed onto theimprintable medium. The beam of actinic radiation 29 passes through afocal area or focal point 30 (focal area if the actinic radiation output28 is an extended output; focal point if the actinic radiation output 28is a point source). The lens 32, which is located some distance beyondthe focal point 30, is arranged to collimate the actinic radiation beam29, and to direct it through the imprint template holder 26 and imprinttemplate 24 onto the imprintable medium.

The actinic radiation beam 29 passes through the focal point or focalarea 30 in order to allow the tip-tilt mirror 36 to be provided abovethe imprint template holder 26, without the actinic radiation beam 29hitting the tip-tilt mirror. Other arrangements of the actinic radiationand the tip-tilt mirror 36 may be used. For example, the tip-tilt mirrormay be provided in some other location, and/or a beam-directingapparatus other than a tip-tilt mirror may be used to direct thealignment radiation beam 35 towards the imprint template. For example, alens system, mirror array or other optical device may be used. Theactinic radiation output may be provided in a different location, withthe actinic radiation beam being directed to the imprint template forexample by beam steering mirrors.

The actinic radiation beam 29 cures the imprintable medium, and therebycauses it to solidify. Once curing has taken place, the imprint template24 and substrate 20 are separated. The substrate table 22 (and/orimprint template holder 26) is then moved in the x or y direction untila different target portion (e.g. a different die) of the substrate 20 islocated beneath the imprint template 24. The alignment and imprintingprocess is then repeated.

The alignment gratings 42-45 are diffraction gratings. They may, forexample, have a pitch of 400 nm. Referring to FIG. 3, during thealignment process, adjacent alignment gratings 42, 44 may be separatedby, for example, 2 microns or less. This is sufficiently close that theadjacent alignment gratings couple with each other to form a compositediffraction grating. Another way of expressing this is to say that adiffraction order from one alignment grating 42 acts as a newillumination beam for the other alignment grating 44, which results inan interplay of propagating diffraction orders between the alignmentgratings.

As a result of the coupling of the adjacent alignment gratings 42, 44 toform a composite diffraction grating, the intensity of the 0thdiffraction order (specular reflection) becomes a periodic function ofthe relative x-positions of the adjacent alignment gratings 42, 44.Since the substrate 20 moves in a scanning motion in the x-direction (oris modulated in the x-direction) during alignment, this periodicfunction gives rise to modulation of the intensity of the diffractedalignment radiation. This intensity-modulated diffracted alignmentradiation passes via the tip-tilt mirror 36 and the beam splitter 38 tothe detector 40. The measured signal may be used by the processor 46 todetermine the position of the substrate alignment grating 44 relative tothe imprint template alignment grating 42. This can, for example, bedone by fitting a set of sinusoidal and cosinusoidal functions to themeasured signal in a manner that is known to a person skilled in theart. The substrate 20 may then, for example, be moved in the x-directionsuch that it is in the aligned position (in the x-direction) withrespect to the imprint template 24.

The measured signal may include noise arising from variations in theseparation between the imprint template alignment grating 42 and thesubstrate alignment grating 44. A signal measured at a longer wavelengthwill vary according to the separation between the imprint templatealignment grating 42 and the substrate alignment grating 44, and cantherefore be used to remove (or reduce) the noise from the signalmeasured at the shorter wavelength.

It is desirable to be able to imprint different patterns using theimprint lithography apparatus. In order to allow the imprint ofdifferent patterns, an imprint template 24 may be removed from theimprint template holder 26 and may be replaced with a different imprinttemplate. The accuracy with which the imprint template 24 is positionedin the imprint template holder 26 may be relatively low, for example bein the range of 40 to 100 microns. Given the relatively low accuracywith which the imprint template 24 is positioned in the imprint templateholder 26, it may be necessary to determine the positions of the imprinttemplate alignment gratings 42, 43 in order to ensure that they arecorrectly illuminated by the alignment radiation beam 35.

In an embodiment, the alignment radiation beam 35 has a cross-sectionaldimension, e.g., diameter, of around 20 microns and thus provides a‘measurement spot’ with a cross-sectional dimension of around 20 microns(the ‘measurement spot’ is the area illuminated by the alignmentradiation beam). The imprint template alignment gratings 42, 43 maymeasure 40×40 microns. It is desirable for the measurement spot of thealignment radiation beam 35 to lie fully within the imprint templatealignment gratings 42, 43, in order to provide optimum alignmentresults. Thus, it is desirable to measure the positions of the imprinttemplate alignment gratings 42, 43 in order to ensure that themeasurement spot is located within the imprint template alignmentgratings when alignment measurements are being performed.

In order to determine the positions of the imprint template alignmentgratings 42, 43, the tip-tilt mirror 36 is moved such that themeasurement spot of the alignment radiation beam 35 scans over an areaon the imprint template in which an imprint template alignment gratingis expected to be found. This scanning of the measurement spot using thetip-tilt mirror 36 may, for example, be controlled by the controller 46.The scanning of the measurement spot may be a raster scan (althoughother scan types may be used).

The area over which the measurement spot is scanned is sufficientlylarge that the imprint template alignment grating is expected to fallwithin that area. The size of the area may take into account theaccuracy with which the imprint template 24 is positioned in the imprinttemplate holder 26. The detector 40 detects radiation which is reflectedfrom the imprint template as a function of the position of themeasurement spot.

The imprint template alignment gratings 42, 43 may have a reflectancewhich differs from the reflectance of other areas of the imprinttemplate. The imprint template alignment gratings may thus be identifiedby comparing the intensity of the detected radiation reflected fromdifferent locations within the area. This comparison may be performed bythe processor 46.

The reflected radiation may be monitored for an intensity which isexpected when the imprint template alignment gratings 42, 43 areilluminated. The expected intensity of reflected radiation may bedetermined, for example, using a calibration measurement, or may be, forexample, calculated based upon the reflectance of the imprint templatealignment gratings. The imprint template gratings may be identified bycomparing the intensity of the detected radiation with the expectedintensity. This comparison may be performed by the processor 46.

Either of the above comparisons may be performed. Alternatively, both ofthe comparisons may be performed.

FIG. 6 shows schematically viewed from above, part of an imprinttemplate which comprises a product pattern 50 (i.e. a pattern which willform part of an integrated circuit or other device when imprinted onto asubstrate). FIG. 6 also shows an imprint template alignment grating 42comprising a grating 42 a which extends in the x-direction and a grating42 b which extends in the y-direction.

FIG. 7 shows a measured intensity image of the part of the imprinttemplate shown in FIG. 6. The measured intensity image is created bymonitoring the intensity of radiation detected by the detector 40 as afunction of the position of the measurement spot of the alignmentradiation beam 35 on the imprint template. As can be seen from FIG. 7,the x-direction grating 42 a and the y-direction grating 42 b areclearly distinguishable from the product pattern 50, and are clearlydistinguishable from each other. Thus, the measured intensity image maybe used to determine the locations of the x-direction grating 42 a andthe y-direction grating 42 b (i.e. the position of the imprint templatealignment grating 42).

The intensity measurement may be performed at a plurality ofwavelengths. Using a plurality of wavelengths may improve the accuracyand/or robustness with which the position of the imprint templatealignment grating 42 is determined. The reflectance of the imprinttemplate alignment grating 42 as a function of wavelength may be known.This information may be stored and used by the processor 46 forwavelengths of radiation included in the alignment radiation beam 35.

Similarly, the intensity measurement may be performed for a plurality ofpolarizations (a plurality of polarizations may be used in the alignmentradiation beam 35). The reflectance of the x-direction grating and they-direction grating as a function of polarization may be known, and maybe stored and used by the processor 46. This information may be storedand used by the processor 46 for polarizations which are included in thealignment radiation beam 35.

The processor 46 may look within the measured intensity image forlocations which match with (or correspond to within a certain threshold)expected intensity values for imprint template alignment marks. Theprocessor 46 may take into account wavelengths and polarizations used inthe alignment radiation beam 35.

Referring again to FIG. 7, the measured intensity image has beenobtained using an alignment radiation beam which is polarized in they-direction. The y-polarized radiation is reflected by the x-directiongrating 42 a and gives rise to a high intensity area in the image,whereas the y-direction polarized radiation is not reflected by they-direction grating 42 b and gives rise to a low intensity area in theimage. Thus, the measured intensity image allows identification of thex-direction grating 42 a and the y-direction grating 42 b.

Measurement of the position of the imprint template alignment gratings42, 43 may be performed without a substrate being present in the imprintlithography apparatus. In an embodiment, a mirror may be located on thesubstrate table 22 when the positions of the imprint template alignmentgratings 42, 43 are being measured. The mirror may increase the amountof alignment radiation received by the detector 40, and thereforeimprove the signal to noise ratio of the measurement. The mirror may,for example, have the same or similar dimensions as a substrate.

The position of each imprint template alignment grating present on theimprint template may be measured using the above described method.Alternatively, the position of a subset of the imprint templatealignment gratings may be measured, the positions of other imprinttemplate alignment gratings being calculated based upon the measuredposition(s) of the subset of imprint template alignment gratings.

The embodiment of the apparatus shown in FIG. 2 has a single output 34,a single tip-tilt mirror 38 and a single detector 40. However, more thanone output, tip-tilt mirror and detector may be provided in thelithographic apparatus. For example, two, three, four or more outputs,tip-tilt mirrors and detectors may be provided in the lithographicapparatus. The number of outputs, tip-tilt mirrors and detectors maycorrespond with the number of alignment gratings present on the imprinttemplate 24. In some instances, the same output may be used for morethan one tip-tilt mirror and detector. An advantage which may arise fromhaving separate tip-tilt mirrors and detectors for each alignmentgrating is that the angle of incidence of the alignment radiation beamon the alignment grating may be lower than would be the case for exampleif a single tip-tilt mirror and detector were to be used, therebyproviding higher accuracy measurements. The alignment radiation beamsmay be substantially perpendicularly incident upon the alignmentgratings.

The positions of the imprint template alignment gratings may be measuredeach time an imprint template 24 is loaded into the imprint templateholder 26. Since this happens relatively infrequently, the time requiredfor the measurement to be performed does not have a significant impactupon the throughput of the imprint lithography apparatus.

The tip-tilt mirror 38 is an example of a beam directing apparatus. Anyother suitable beam directing apparatus may be used. The beam directingapparatus may be controlled by the controller 48.

The imprint template alignment grating 42 is an example of an imprinttemplate alignment mark. Embodiments of the invention may be used todetermine the position of any suitable imprint template alignment mark.

Embodiments of the invention use a detector 40 to detect radiation whichhas been reflected from the imprint template alignment mark. This isadvantageous because it allows the same detector 40 to be used that willsubsequently be used to measure alignment of the imprint template 24 andsubstrate 20. In an alternative embodiment, a detector (not shown) maybe located beneath the imprint template 24, and may be used to measurealignment radiation which is transmitted by the imprint templatealignment mark.

Embodiments of the invention allow the positions of imprint templatealignment marks to be measured without adding any additional hardware tothe imprint lithography apparatus (the hardware which is used is alreadypresent in order to provide alignment of the substrate and the imprinttemplate). Embodiments of the invention may therefore be cheaper andsimpler than using an additional detector such as an imaging detector todetermine the positions of the imprint template alignment marks.

An embodiment of the invention may scan the imprint template 24 relativeto the alignment radiation beam 35, instead of (or in addition to)scanning the alignment radiation beam relative to the imprint template.

An embodiment of the invention may be used to obtain coarse alignment ofthe substrate 20 relative to the imprint template 24. As mentionedfurther above, when alignment is to take place, the substrate table 22is moved until a target portion (e.g. a die) of the substrate 20 ispositioned beneath the imprint template 24, and the imprint templatealignment gratings 42, 43 are located over the substrate alignmentgratings 44, 45. The accuracy with which the substrate table ispositioned in this initial alignment phase is such that the imprinttemplate alignment gratings 42, 43 and substrate alignment gratings 44,45 are positioned sufficiently accurately to allow alignment (sometimesreferred to as fine alignment) to be performed. In order to ensure thatthe accuracy of the initial alignment phase is sufficient, so calledcoarse alignment of the substrate 20 to the imprint template 24 may beperformed. Coarse alignment may be performed when the substrate isloaded into the imprint lithography apparatus.

Coarse alignment of the substrate to the imprint template shouldposition the substrate such that the substrate alignment gratings 44, 45are within the capture range of the imprint template alignment gratings42, 43. The term ‘capture range’ is intended to mean the range ofmisalignments of the substrate 20 from the aligned position over whichalignment can be achieved using the alignment gratings 42-45. Thecapture range of an embodiment of the invention may be less than thepitch of the alignment gratings. The capture range may be approximatelya quarter of the pitch of the alignment gratings. Thus, the coarsealignment may determine the position of the substrate alignment gratingswith an accuracy which is greater than the pitch of the alignmentgratings, and which may be greater than a quarter of the pitch of thealignment gratings.

Coarse alignment of the substrate alignment gratings 44, 45 relative tothe imprint template alignment gratings 42, 43 may be achieved using thefollowing method, which is described in relation to FIGS. 8 and 9. FIGS.8 and 9 show schematically, viewed from above, part of a substrate 20upon which four dies 60 have been provided. The dies 60 are separated byscribe lanes 62. A substrate alignment grating is provided in the scribelanes 62, the substrate alignment grating 44 comprising an x-directiongrating 44 a and a y-direction grating 44 b. Also shown is an imprinttemplate alignment grating 42 which comprises an x-direction grating 42a and a y-direction grating 42 b.

Coarse alignment of the substrate 20 relative to the imprint template isperformed separately for the x-direction and the y-direction. Referringfirst to FIG. 8, coarse alignment in the x-direction is obtained bymodulating the position of the substrate 20 in the y-direction at thesame time as moving the substrate in the x-direction (in this case thenegative x-direction as indicated schematically by an arrow 64). They-direction imprint template grating 42 b is illuminated by thealignment radiation beam such that the measurement spot 35 a lies withinthe y-direction imprint template grating 42 b. Alignment radiationreflected from the y-direction imprint template grating is detected bythe detector 40 (see FIG. 2).

When the y-direction substrate grating 44 b is positioned as shown inFIG. 8, there is no overlap between the y-direction substrate grating 44b and the y-direction imprint template grating 42 b. Thus, no modulationof the reflected alignment radiation beam is seen at the detector 40.The y-direction substrate grating 44 b will in due course begin tooverlap with the y-direction imprint template grating 42 b, giving riseto modulation of the reflected alignment radiation beam. The size ofthis overlap will gradually increase, and the amplitude of themodulation will increase accordingly. The overlap will pass through amaximum when the x-direction positions of the gratings 42 b, 44 b arethe same. Following this, the overlap will gradually decrease untilthere is no overlap, with the amplitude of the modulation decreasingaccordingly.

Since the amplitude of the modulation seen by the detector 40 dependsupon the overlap between the y-direction substrate grating 44 b and they-direction imprint template grating 42 b, the maximum modulationindicates alignment of those gratings in the x-direction. The processor46 (see FIG. 2) may determine the maximum modulation via suitableanalysis of the modulated signal. The analysis may, for example, includecurve fitting, interpolation or any other suitable technique. In someinstances, the width of the y-direction substrate grating 44 b maydiffer from the width of the y-direction imprint template grating 42 b.Where this is the case, the modulated signal may have a maximum value inthe form of a plateau. The analysis may determine the center of theplateau.

Once the aligned position in the x-direction of the y-direction gratings42 b, 44 b has been determined, this may be used to determine thealigned position in the x-direction of the neighboring x-directiongratings 42 a, 44 a. The distance in the x-direction between thex-direction substrate grating 44 a and the y-direction substrate grating44 b is known (this is a known property of the substrate). Thus, theposition in the x-direction of the x-direction substrate grating 44 amay be calculated. Similarly, the distance between the x-directionimprint template grating 42 a and the y-direction imprint templategrating 42 b is known (this is a known property of the imprinttemplate). Thus, the positions in the x-direction of the x-directionsubstrate grating 44 a and the x-direction imprint template grating 42 amay be calculated. The positions are calculated with sufficient accuracythat fine alignment of the substrate relative to the imprint templatemay subsequently be achieved using the x-direction gratings 42 a, 44 a.In other words, coarse alignment in the x-direction has been achieved.

The same approach may be used to achieve coarse alignment of thex-direction imprint template grating 42 a and the x-direction substrategrating 44 a (and therefrom the y-direction imprint template grating 42b and the y-direction substrate grating 44 b). Referring to FIG. 9,coarse alignment in the y-direction is obtained by modulating theposition of the substrate 20 in the x-direction at the same time asmoving the substrate in a scanning motion in the y-direction (in thiscase in the negative y-direction as indicated schematically by an arrow64). The x-direction imprint template grating 42 a is illuminated by thealignment radiation beam such that the measurement spot 35 a lies withinthe x-direction imprint template grating 42 a. Alignment radiationreflected from the x-direction imprint template grating 42 a is detectedby the detector 40 (see FIG. 2).

When the x-direction substrate grating 44 a is positioned as shown inFIG. 9, there is no overlap between the x-direction substrate grating 44a and the x-direction imprint template grating 42 a. Thus, no modulationof the reflected alignment radiation beam is seen at the detector 40.The x-direction substrate grating 44 a will in due course begin tooverlap with the x-direction imprint template grating 42 a, giving riseto modulation of the reflected alignment radiation beam. The size ofthis overlap will gradually increase, and the amplitude of themodulation will increase accordingly. The overlap will pass through amaximum when the y-direction positions of the gratings 42 a, 44 a arethe same. Following this, the overlap will gradually decrease untilthere is no overlap, with the amplitude of the modulation decreasingaccordingly.

Since the amplitude of the modulation seen by the detector 40 dependsupon the overlap between the x-direction substrate grating 44 a and thex-direction imprint template grating 42 a, the maximum modulationindicates alignment of those gratings in the y-direction. The processor46 (see FIG. 2) may determine the maximum modulation via suitableanalysis of the modulated signal. The analysis may, for example, includecurve fitting, interpolation or any other suitable technique.

Once the aligned position in the y-direction of the x-direction gratings42 a, 44 a has been determined, this may be used to determine thealigned position in the y-direction of the y-direction gratings 42 b, 44b. The distance in the y-direction between the y-direction substrategrating 44 b and the x-direction substrate grating 44 a is known (thisis a known property of the substrate). Thus, the position in they-direction of the y-direction substrate grating 44 b may be calculated.Similarly, the distance between the y-direction imprint template grating42 b and the x-direction imprint template grating 42 a is known (this isa known property of the imprint template). Thus, the positions in they-direction of the y-direction substrate grating 44 b and they-direction imprint template grating 42 b may be calculated. Thepositions are calculated with sufficient accuracy that fine alignment ofthe substrate relative to the imprint template may subsequently beachieved using the y-direction gratings 42 b, 44 b. In other words,coarse alignment in the y-direction has been achieved.

The modulation 64 which is shown in FIGS. 8 and 9 has been exaggeratedfor the purpose of illustration. In practice, the modulation may besmaller than the pitch of the alignment gratings 42 a,b, 44 a,b. Themodulation may be, for example, less than or equal to half the pitch ofthe alignment gratings, less than or equal to a quarter of the pitch ofthe alignment gratings, or smaller than that. In an embodiment, thepitch of the alignment gratings may be around 500 nanometers, and theamplitude of the modulation may be 100 nm or less. The modulation may,for example, have a frequency of around 1 kHz.

It is not necessary that the direction of the modulation isperpendicular to the direction of movement of the substrate. Thedirection of modulation should include a component which isperpendicular to the direction of movement of the substrate. Forexample, referring to FIG. 8, the direction of movement is thex-direction. The modulation need not be in the y-direction, but shouldinclude a component which is in the y-direction.

Although the above description refers to performing coarse alignment inthe x-direction, and then performing coarse alignment in they-direction, coarse alignment in the y-direction may be performed beforecoarse alignment in the x-direction.

Coarse alignment of the substrate and the imprint template may beachieved using the method described above each time a substrate 20 isloaded into the imprint lithography apparatus. Once coarse alignment hasbeen achieved, the positions of alignment gratings across the substrate20 may be known with sufficient accuracy to allow fine alignment of theimprint template 24 to be achieved across the substrate (e.g. finealignment of the imprint template to dies 60 on the substrate).

In some instances, the method described above may be repeated forsubstrate alignment gratings at a second location on the substrate 20.Where this is done, coarse alignment measurements are obtained for twodifferent locations on the substrate 20, the two locations being spacedapart on the substrate. These two coarse alignment measurements may beused to obtain more accurate coarse alignment, which may for examplecorrect for rotation of the substrate.

In some instances, the method described above may be repeated forsubstrate alignment gratings at three or more different locations on thesubstrate 20, thereby providing more accurate coarse alignment.

In an embodiment, the method described above may be repeated forsubstrate alignment gratings at four different locations on thesubstrate 20. Calculations for the four alignment gratings may beperformed simultaneously, for example using a model which is solved. Theresult of the calculation may provide coarse alignment which takes intoaccount translation in the x and y directions, rotation, and expansionof the substrate.

Since the method is used a relatively small number of times persubstrate, the impact of the method on the speed at which substrates maybe imprinted by the imprint lithography apparatus is relatively low.

The embodiment of the apparatus shown in FIG. 2 has a single output 34,a single tip-tilt mirror 38 and a single detector. However, more thanone output, tip-tilt mirror and detector may be provided in thelithographic apparatus. For example, two, three, four or more outputs(e.g., two, three, four or more sources), tip-tilt mirrors and detectorsmay be provided in the lithographic apparatus. Thus, coarse alignmentmeasurements may be obtained simultaneously at more than one location.In an embodiment, a plurality of coarse alignment measurements in thex-direction may be obtained simultaneously, followed by a plurality ofcoarse alignment measurements in the y-direction (or vice-versa).

The coarse alignment may be sufficiently accurate that it providesalignment of substrate alignment gratings and imprint template alignmentgratings to within one alignment grating period (i.e. provides anaccuracy which is finer than the pitch of the alignment gratings). In anembodiment, the pitch of the alignment gratings may be 500 nm, and theaccuracy of the coarse alignment may be better than 500 nm.

An advantage provided by the coarse alignment method described above isthat it does not require any additional hardware to be provided in theimprint lithography apparatus (the hardware which is used is the samehardware that is used by the fine alignment method).

The coarse alignment method should align the substrate 20 and theimprint template 24 to within the capture range provided by thealignment gratings 23, 24. The term ‘capture range’ is intended to meanthe range of misalignments from over which alignment can be achievedusing the alignment gratings. The capture range of an embodiment may beless than or equal to the pitch of the alignment gratings. The capturerange may be approximately a quarter of the pitch of the alignmentgratings 23, 24. This link between the capture range and the gratingpitch may influence the grating pitch which is used. A smaller gratingpitch may provide more accurate fine alignment, but may require a higheraccuracy of coarse alignment, in order to ensure that the coarsealignment aligns the alignment gratings within the capture range.

In some instances it may be possible to increase the capture range ofthe alignment gratings without giving rise to a corresponding reductionof the accuracy of fine alignment which may be achieved.

Referring to FIG. 10, an alignment grating 70 may comprise a lowresolution grating, lines of the low resolution grating being formedfrom high resolution gratings. In this context the term ‘low resolution’is intended to mean a resolution which is lower than the resolution ofthe ‘high resolution’ grating. Similarly, the term ‘high resolution’ isintended to mean a resolution which is higher than the resolution of the‘low resolution’ grating. Neither term is intended to imply a specificresolution. The low resolution grating comprises a set of lines 71 whichare referred to hereafter as thick lines 71. Each of the thick lines 71comprises a set of lines 72, hereafter referred to as thin lines 72. Thethin lines 72 extend in substantially the same direction as the thicklines 71. The thick lines 71 of the grating 70 may be used to obtaincoarse alignment over a large capture range. The thin lines 72 of thealignment grating 70 may then be used to obtain fine alignment with highresolution. The pitch of the thick lines 71 may be, for example,selected from the range of 5 to 10 microns, and the pitch of the finelines 72 may be, for example, selected from the range of 500 to 1000 nm.Other pitches may be used. The alignment grating 70 may be provided onan imprint template.

A further approach to extending the capture range of an alignmentgrating is shown in FIG. 11. A first alignment grating 73 compriseslines 74 extending in the x-direction (hereafter referred to as thicklines), which are formed from gratings comprising lines 75 which extendin the y-direction (hereafter referred to as thin lines). A secondalignment grating 76 comprises lines 77 extending in the y-direction(hereafter referred to as thick lines) which are formed from gratingscomprising lines 78 which extend in the x-direction (hereafter referredto as thin lines). The thin lines extend in a direction which issubstantially transverse to the direction of the thick lines. The thicklines 74 of the first alignment grating 73 may be used to provide coarsealignment over a large capture range in the x-direction. The thin lines78 of the second alignment grating 76 may then be used to obtain finealignment in the x-direction. Similarly, the thick lines 77 of thesecond alignment grating may be used to obtain coarse alignment in they-direction, and the thin lines 75 of the first alignment grating 73 maybe used to obtain fine alignment in the y-direction. The pitch of thethick lines 74, 77 may be, for example, selected from the range of 5 to10 microns. The pitch of the thin lines 75, 78 may be, for example,selected from the range of 500 to 1000 nm. Other pitches may be used.The alignment gratings 73, 76 may be provided on an imprint template.

Alignment radiation which is used to illuminate the alignment gratings73, 76 of FIG. 11 may have a linear polarization. When fine alignment isbeing performed in a given direction, the polarization of the alignmentradiation beam may be parallel to the thin lines which extend in thatdirection. Where this is done, a portion of the alignment radiation maypropagate through gaps between the thin lines, thereby allowing finealignment to be performed. When coarse alignment is being performed in agiven direction, the polarization of the alignment radiation beam may beperpendicular to the thin lines which extend in that direction. This maycause the thin lines to appear opaque to the alignment radiation,thereby improving the contrast which is provided by the thick lines(compared with the contrast that would be obtained if the alignmentradiation was polarized parallel to the thin lines).

A further arrangement for increasing the capture range of the alignmentgratings is shown in FIGS. 12 and 13. FIG. 12 shows an imprint template24 which has been provided with first and second imprint templatealignment gratings 80 a, 80 b, and a substrate 20 which has beenprovided with first and second substrate alignment gratings 81 a, 81 b.The pitch of the first imprint template alignment grating 80 a issmaller than the pitch of the second imprint template alignment grating80 b. Similarly, the pitch of the first substrate alignment grating 81 ais smaller than the pitch of the second substrate alignment grating 81b. As can be seen from FIG. 12, when the substrate 20 and the imprinttemplate 24 are aligned, the first and second imprint template alignmentgratings 80 a, 80 b are aligned respectively with the first and secondsubstrate gratings 81 a, 81 b.

Referring to FIG. 13, when the substrate 20 and the imprint template 24are not aligned, the misalignment between the first imprint templatealignment grating 80 a and the first substrate alignment grating 81 adiffers from the misalignment between the second imprint templatealignment grating 80 b and the second substrate alignment grating 81 b.Analysis of the difference between the misalignments may allow themisalignment of the substrate 20 relative to the imprint template 24 tobe calculated, thereby increasing the capture range of the alignmentgratings (compared with the capture range that would be provided if thealignment gratings all had the same pitch).

The alignment radiation beam 35 may be a laser beam generated by a laser34. The laser may be configured to generate alignment radiation at aplurality of wavelengths, which may include one or more visiblewavelengths and one or more infrared wavelengths. Optics may be includedin the laser 34, or downstream from the laser, which may be used toselect or apply different polarizations to the alignment radiation beam35.

The substrate alignment gratings 44, 45 may be partially reflective. Theimprint template alignment gratings 42, 43 may be partially reflective.

The imprint template may be an imprint template which is sufficientlylarge to pattern an entire substrate in one go. Alternatively, multipleimprints of the imprint template onto the substrate may be required inorder to pattern the substrate.

In the described embodiments, alignment (both coarse alignment and finealignment) is achieved by moving the substrate table 20 in the x and ydirections. However, it is possible to move the imprint template 24 inthe x and y directions to achieve alignment. This may be done insteadof, or as well as, movement of the substrate table 20 in the x and ydirections. In general terms, it may be said that there is relativemovement between the substrate and the imprint template.

Cartesian coordinates are shown in FIGS. 2 to 13 in order to facilitateexplanation of those figures. The Cartesian coordinates followlithographic convention, with the x and y directions being in the planeof the substrate 20, and the z-direction being perpendicular to theplane of the substrate. The Cartesian coordinates are not intended toimply that the substrate or the imprint template must have any specificorientation. Movements in the x and y directions may be considered to beexamples of lateral movement (lateral movement may be considered to meanmovement in a plane which is parallel or substantially parallel to thesurface of the substrate).

Although described embodiments of the invention use UV imprintlithography, an embodiment of the invention may use other forms ofimprint lithography such as hot imprint lithography.

The present invention relates to imprint lithography apparatus andmethods. The apparatus and/or methods may be used for the manufacture ofdevices, such as electronic devices and integrated circuits or otherapplications, such as the manufacture of integrated optical systems,guidance and detection patterns for magnetic domain memories, flat-paneldisplays, liquid-crystal displays (LCDs), thin film magnetic heads,organic light emitting diodes, etc.

In this specification, the term “substrate” is meant to include anysurface layers forming part of the substrate, or being provided onanother substrate, such as planarization layers or anti-reflectioncoating layers.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, an embodiment of the invention may takethe form of a computer program containing one or more sequences ofmachine-readable instructions configured to cause performance of amethod as disclosed above, or a computer-readable data storage medium(e.g. semiconductor memory, magnetic or optical disk) having such acomputer program stored therein.

In the above embodiments, the lithography apparatus comprises a singleimprint template. Thus, a single imprint template, a single imprinttemplate holder, a single substrate holder and a single substrate isprovided in a single chamber. In other embodiments, more than oneimprint template, more than one imprint template holder, more than onesubstrate holder, and/or more than one substrate may be provided in oneor more chambers, in order for imprints to be undertaken moreefficiently or quickly (e.g. in parallel). For example, in anembodiment, there is provided an apparatus that includes a plurality(e.g. 2, 3, or 4) of substrate holders. In an embodiment, there isprovided an apparatus that includes a plurality (e.g. 2, 3, or 4) ofimprint templates or imprint template holders. In an embodiment, thereis provided an apparatus configured to use one template holder persubstrate holder. In an embodiment, there is provided an apparatusconfigured to use more than one template holder per substrate holder. Inan embodiment, there is provided an apparatus that includes a plurality(e.g. 2, 3, or 4) of imprintable medium dispensers. In an embodiment,there is provided an apparatus configured to use one imprintable mediumdispenser per substrate holder. In an embodiment, there is provided anapparatus configured to use one imprintable medium dispenser per imprinttemplate holder. In an embodiment, where an apparatus is provided thatincludes a plurality of substrate holders, the substrate holders mayshare functionalities in the apparatus. For instance, the substrateholders may share a substrate handler, a substrate cassette, a gassupply system (e.g. to create a helium environment during imprinting),an imprintable medium dispenser, and/or a radiation source (for curingthe imprintable medium). In an embodiment, two or more of the substrateholders (e.g. 3 or 4) share one or more functionalities of the apparatus(e.g. 1, 2, 3, 4, or 5 functionalities). In an embodiment, one or morefunctionalities (e.g. 1, 2, 3, 4, or 5) of the apparatus are sharedamong all substrate holders.

The descriptions above are intended to be illustrative, not limiting,Thus, it will be apparent to those skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A method of determining a position of animprint template held by an imprint template holder in an imprintlithography apparatus, the imprint lithography apparatus comprising ahardware processor and a non-transitory computer-readable mediumcontaining one or more machine-readable instructions and the methodcomprising: causing, by the one or more machine-readable instructionswhen executed by the hardware processor, relative movement between theimprint template and an alignment radiation beam as it is provided froman alignment beam outlet of the imprint lithography apparatus so as toilluminate a first area of the imprint template in which an alignmentmark is expected to be found and illuminate a second area of the imprinttemplate not having any alignment feature of the alignment mark within across-section of the alignment radiation beam as impinged on the secondarea; identifying, by the one or more machine-readable instructions whenexecuted by the hardware processor, a position of the alignment mark viaanalysis of the intensity detected by a detector of the imprintlithography apparatus of radiation reflected or transmitted from thefirst and second areas; and after determination of the position of thealignment mark, both causing, by the one or more machine-readableinstructions when executed by the hardware processor, use of theposition to provide the alignment mark in a path of the alignmentradiation beam and causing, by the one or more machine-readableinstructions when executed by the hardware processor, measurement ofalignment with the alignment radiation beam using the alignment mark anda corresponding substrate alignment mark.
 2. The method of claim 1,wherein the analysis of the detected intensity comprises comparing theintensity of detected radiation reflected from different locationswithin the first and second areas.
 3. The method of claim 1, wherein theanalysis of the detected intensity comprises comparing the intensity ofdetected radiation with an intensity which is expected when thealignment mark is illuminated.
 4. The method of claim 1, wherein aplurality of wavelengths of the alignment radiation beam are separatelydetected and analyzed.
 5. The method of claim 1, wherein a plurality ofpolarizations of the alignment radiation beam are separately detectedand analyzed.
 6. The method of claim 1, wherein the relative movementcomprises a raster scan.
 7. The method of claim 1, wherein the alignmentmark is a grating.
 8. An imprint lithography apparatus comprising: animprint template holder configured to hold an imprint template; analignment radiation beam outlet; a detector; a hardware processor; and anon-transitory computer-readable medium containing one or moremachine-readable instructions that when executed by the hardwareprocessor: cause relative movement between the imprint template and analignment radiation beam as it is provided by the alignment radiationbeam outlet, such that the alignment radiation beam illuminates a firstarea of the imprint template not having any alignment feature of analignment mark within a cross-section of the alignment radiation beam asimpinged on the first area and illuminates a second area of the imprinttemplate in which the alignment mark is expected to be found, identify aposition of the alignment mark via analysis of intensity detected by thedetector of radiation reflected or transmitted from the first and secondareas, and after determination of the position of the alignment mark,both cause use of the position to provide the alignment mark in a pathof the alignment radiation beam and cause measurement of alignment withthe alignment radiation beam using the alignment mark and acorresponding substrate alignment mark.
 9. The apparatus of claim 8,further comprising a beam directing apparatus and wherein theinstructions when executed by the hardware processor cause the relativemovement by instructing the beam directing apparatus to scan thealignment radiation beam such that the alignment radiation beamilluminates the first and second areas.
 10. The apparatus of claim 8,wherein the instructions when executed by the hardware processor furthercause the hardware processor to compare the intensity of detectedradiation when different locations within the first and second areas areilluminated.
 11. The apparatus of claim 8, wherein the instructions whenexecuted by the hardware processor further cause the hardware processorto compare the intensity of detected radiation with an intensity whichis expected when the alignment mark is illuminated.
 12. The apparatus ofclaim 8, comprising an alignment radiation beam source configured toprovide the alignment radiation beam at a plurality of wavelengths, andwherein the detector is configured to separately detect the plurality ofwavelengths and the instructions when executed by the hardware processorfurther cause the hardware processor to analyze the separately detectedwavelengths.
 13. The apparatus of claim 8, comprising an alignmentradiation beam source configured to provide the alignment radiation beamat a plurality of polarizations, and wherein the detector is configuredto separately detect the plurality of polarizations and the instructionswhen executed by the hardware processor further cause the hardwareprocessor to analyze the separately detected polarizations.
 14. Theapparatus of claim 8, comprising a beam directing apparatus configuredto scan the alignment radiation beam in a raster scan.
 15. The apparatusof claim 8, wherein the alignment mark is a grating.
 16. A method ofobtaining alignment of a substrate held by a substrate holder in animprint lithography apparatus, and an imprint template held by animprint template holder in the imprint lithography apparatus, theimprint lithography apparatus comprising a hardware processor and anon-transitory computer-readable medium containing one or moremachine-readable instructions and the method comprising: causing, by theone or more machine-readable instructions when executed by the hardwareprocessor, relative movement between the substrate and the imprinttemplate in a first lateral direction, and providing a modulationmovement between the substrate and the imprint template in a secondlateral direction, which includes a component that is perpendicular tothe first lateral direction, during the relative movement; causing, bythe one or more machine-readable instructions when executed by thehardware processor, illumination by an alignment radiation beam outletof the imprint lithography apparatus of the imprint template alignmentgrating during the relative movement and the modulation movement;determining, by the one or more machine-readable instructions whenexecuted by the hardware processor, a modulation of detected reflectedalignment radiation when the imprint template alignment grating and thesubstrate alignment grating overlap, the detected reflected alignmentradiation detected by a detector of the imprint lithography apparatus,the detector configured to detect radiation reflected from the imprinttemplate alignment grating and the substrate alignment grating; anddetermining, by the one or more machine-readable instructions whenexecuted by the hardware processor, a maximum overlap between thesubstrate alignment grating and the imprint template alignment gratingbased on the determined modulation, the maximum overlap providingalignment of the substrate and the imprint template.
 17. The method ofclaim 16, wherein: the imprint template alignment grating has a knownseparation in the first lateral direction from a further imprinttemplate alignment grating, and the substrate alignment grating has aknown separation in the first lateral direction from a further substratealignment grating; and the method further comprises determining analigned position of the further imprint template alignment grating andthe further substrate alignment grating based upon the relativepositions of the substrate and the imprint template when the maximumoverlap occurred.
 18. The method of claim 16, wherein the amplitude ofthe modulation movement in the second lateral direction is smaller thanthe pitch of the imprint template and substrate alignment gratings. 19.The method of claim 18, wherein the amplitude of the modulation movementin the second lateral direction is less than or equal to half of thepitch of the imprint template and substrate alignment gratings.
 20. Themethod of claim 16, wherein the method is repeated in a substantiallyperpendicular lateral direction.
 21. An imprint lithography apparatuscomprising: an imprint template holder configured to hold an imprinttemplate and a substrate holder configured to hold a substrate; analignment radiation beam outlet configured to illuminate an imprinttemplate alignment grating; a detector configured to detect radiationreflected from the imprint template alignment grating and an adjacentsubstrate alignment grating; and a hardware processor; and anon-transitory computer-readable medium containing one or moremachine-readable instructions that when executed by the hardwareprocessor: cause relative movement between the substrate and the imprinttemplate in a first lateral direction, and provide a modulation movementbetween the substrate and the imprint template in a second lateraldirection, which includes a component that is perpendicular to the firstlateral direction, during the relative movement, cause illumination ofthe imprint template alignment grating during the relative movement andthe modulation movement, determine a modulation of the detectedreflected alignment radiation when the imprint template alignmentgrating and the substrate alignment grating overlap, and determine amaximum overlap between the substrate alignment grating and the imprinttemplate alignment grating based on the determined modulation, themaximum overlap providing alignment of the substrate and the imprinttemplate.